The invention relates to a plastic snap cage for radial ball bearings which includes of thin-walled cup-like pocket elements that are distributed about the circumference, with the pocket elements being connected with each other by ribs to form a single piece. The so formed pockets are open in the axial direction to accept the balls.
Various designs of snap cages for ball bearings, which are cages with pockets that have lateral openings in the axial direction, are known in the art. Typically, snap cages have a continuous solid side ring on one side and cup-like pocket elements with slots or openings between the pockets on the other side. These pocket elements can yield elastically, allowing the bearing balls to be easily snapped into position.
A snap cage of this type for balls is known, for example, from the German utility model application DE-GM 19 10 797. The cage disclosed therein includes thin-wall, cup-like pocket elements, also referred to as guide cups, which are open on one side in the axial direction, and ribs that connect these guide cups.
These cages disadvantageously tend to have sharp transitions and are therefore easily nicked, i.e., they can break. As another disadvantage, the sharp edges of the cage that surround the bearing balls tend to disrupt the lubricating film that adheres to the bearing balls.
It is therefore an object of the invention to provide a cage of this type which is less susceptible to breakage and at the same time improves the operation of the ball bearing.
The object is solved according to the invention in that at least the radially inwardly and/or the radially outwardly extending boundary edges of the pockets are rounded in accordance with a selected rounding radius R.
The proposed design of the snap cage in accordance with the invention firstly improves the tribological conditions in the ball bearing since the rounded boundary edges of the pockets have less of a detrimental effect on the lubricating film that adheres to the bearing balls than sharp boundary edges. Secondly, the ball bearing is easier to assemble because the bearing balls can be resiliently inserted in the cage not only, as up to now, in the axial direction, but also in the radial direction either from above downwardly or from below upwardly. Thirdly, rounding of the boundary edges advantageously also reduces the risk of breakage considerably, in particular for small filigree cages. Finally and fourthly, the cage can advantageously be manufactured with a higher surface quality which makes it easier to assemble the bearing.
According to another feature of the present invention the boundary edges of the pockets that are disposed along the circumference and face each other may be rounded. The rounded edges allow the pockets that are open in one direction to yieldably deflect in the axial direction.
According to another feature of the present invention, the rounding radius should be xc2x10.05 mm. This is the smallest possible radius. The magnitude of the radius, however, depends on the available installation space, the diameter of the balls and the type of guidance of the cage. Rounding radii in the range of several millimeters are also feasible.
According to another feature of the invention, the snap cage can be packed with a filler material and/or made of a glass fiber reinforced polyamide (PA). Typical filler materials known in the art are to be understood broadly as including additives of various structures which provide the cage with the desired properties and thus enhance the performance of the roller bearing, for example, fibers of all types, glass spheres, but also graphite or molybdenum sulfide. Polyamides are thermoplastic materials known to those skilled in the art due to their advantageous mechanical properties. More specifically, polyamides retain their shape at elevated temperatures and are very resistant to fuel and lubricants. The mechanical properties can be further improved by adding glass fibers, thereby increasing both the rigidity and the softening temperature.
The invention will now be described in detail with reference to the following embodiments.